Answer :
The 42.7-gram sample of potassium nitrate contains approximately 16.45 grams of potassium. B) 16.5 grams is the correct option.
To determine the grams of potassium in a sample of potassium nitrate ions, we need to consider the molar mass and the stoichiometry of the compound.
The molar mass of potassium nitrate (KNO₃) can be calculated by summing the atomic masses of its constituent elements:
Molar mass of KNO₃ = (atomic mass of K) + (atomic mass of N) + 3 ×(atomic mass of O)
= (39.10 g/mol) + (14.01 g/mol) + 3 × (16.00 g/mol)
= 101.10 g/mol
Next, we can calculate the grams of potassium (K) in the sample using the molar mass ratio between potassium and potassium nitrate.
Grams of potassium = (mass of potassium nitrate) × (molar mass of K) / (molar mass of KNO₃)
= (42.7 g) × (39.10 g/mol) / (101.10 g/mol)
= 16.45 g
Therefore, the 42.7-gram sample of potassium nitrate contains approximately 16.45 grams of potassium.
Among the given options:
A) 39.1 grams of potassium is not the correct answer as it is the molar mass of potassium, not the grams in the given sample.
B) 16.5 grams of potassium is the correct answer.
C) 21.4 grams and D) 8.54 grams are not the correct answers.
E) none of the above is not the correct answer as B) 16.5 grams is the correct option.
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